Thermographic transfer sheet having a support of a paper and plastic coating and the method of use



Jan. 31, 1967 R. B. RUSSELL 3 1, 9

THERMOGRAPHIC TRANSFER SHEET HAVING A SUPPORT OF A PAPER AND PLASTICCOATING AND THE METHOD OF USE Filed Dec. 2, 1960 PAPFR BACKER K I, DIEDOR PlGMENTED HEAT MELTABLE OATl Ng QXICEQ CO PY\ SHEET l f 5/ XMP l r r.I l

/ MINERAL co An Ne/ I ORIGINAL INVENTOR. Kim 6 BY 13 W36 United StatesPatent 3,301,697 THERMOGRAPI-IIC TRANSFER SHEET HAVING A SUPPORT OF APAPER AND PLASTIC COATING AND THE METHOD OF USE Robert B. Russell, 248Park St., Newton, Mass. 02158 Filed Dec. 2, 1960, Ser. No. 73,245

Claims. (Cl. 119-36.4)

This invention relates to thermographic copying and more particularly toan improved transfer sheet of the type described and claimed genericallyin my prior and copending application Serial No. 68,286, filed November9, 1960, now U.S. Patent 3,131,080, entitled Thermographic CopyingProcess and Transfer Sheet Therefor.

In my said prior application, five species are claimed, and it is myintention herein to claim a sixth species coming within the generalpurview and mode of operation of the invention of that application.

The objects of this invention are essentially to provide an improvedtransfer sheet for use in the process which I call Prestofax and whichis more specifically described in my above said copending application.The salient features of Prestofax which call for a special form oftransfer sheet are: (a) the transfer sheet serves as a tensioning beltto press the copy sheet against the original; (b) the incident radiationstrikes the exposed back side of the transfer sheet; and (c) thetransfer sheet is separated from the copy sheet at a critical momentfollowing irradiation. The object then of this invention is to provide atransfer sheet which is designed specifically for improved performanceunder those special conditions.

In the invention described herein, I accomplish this object by applyingto a paper base a smooth coating of a clear plastic, and thereaftercoating the plastic with a dyed (or pigmented) heat meltable coating.

The advantages of this form of invention are several. The paper baseprovides dimensional stability and resistance to heat. The unreinforcedplastic transfer sheets of FIGS. 2, 3 and 5 of my above-said priorapplication print remarkably well, but they can become weak when heated.This is usually not a serious problem, but during extended periods ofuse the lamp and reflector absorb a great deal of heat, and thereafterwhen the machine is idle this residual heat tends to weaken theunreinforced plastic transfer sheet of those examples. However, when theplastic sheet is laminated to a paper base, as herein described, theresult is a dimensionally stable and heat resistant transfer sheet.

Another advantage of this form of the invention is that the dyed orpigmented heat meltable coating overlies a smooth, relatively uniform,and highly conductive surface which is also made dimensionally stableunder heat by the paper backer. These factors lead to high uniformityand clarity in the printed image.

The single figure shows a simple paper backer carrying a clear plasticcoating or lamination and a dyed or pigmented heat meltable coating,overlying a mineral coated copy sheet, which in turn overlies anoriginal.

The paper base may be any suitable sheet. I have used Monarco (S. D.Warren Co.) with excellent results. A relatively thin, smooth anduniform sheet is desirable, but not required. Cost is probably the majorconsideration in the selection of the paper backer and accordingly, theleast expensive sheet per foot having suflicient strength, whenlaminated, to serve as the tensioning belt in Prestofax is adequate.

The clear plastic coating is also a matter of choice. Regeneratedcellulose, cellulose acetate, PVC, PVA, polystyrene, polyethylene,nylon, Teflon, and Mylar and the like substances are all satisfactory.The main thing is to provide a smooth, homogeneous and highly conductive(as compared to paper) surface to receive the heat meltable coating andits melting point must be substantially higher than that of the heatmeltable coating.

, The heat meltable coating may be a Wax or other similar substance. Ifind that a melting point of about F. to F. is entirely satisfactory.Parafiin and microcrystalline Waxes are suitable. A sharp melting pointis also desirable.

The dye can be any one of numerous dyes, having low infra-redabsorptivity. Various forms of pigment have also been used with success.The type of coloring matter employed is not critical provided it is nothighly absorbent of infra-red radiation. In fact, I intend herein toclaim the heat meltable coating broadly enough to cover it whether ornot it contains coloring matter.

In connection With the use of pigment, I find that a mineral coated copysheet is markedly better than a simple unfilled and uncoated sheet.Apparently the pigment has a filtering action which is particularlysuitable for mineral coated paper. Accordingly, I also intend to claimthis feature specifically herein. In addition, I have found that a sheetwhich is coated only on one side makes markedly better copy when thecoated side is placed facing the original, and I also intend to claimthis combination specifically herein.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

I claim:

1. A transfer sheet for thermographic copying in which the transfersheet serves as a tensioning belt and is exposed to the direct radiationof a source of radiation, said transfer sheet comprising: a paper base,a clear plastic coating on said base, and a heat meltable coating onsaid plastic having a melting point substantially lower than the meltingpoint of said plastic coating.

2. The transfer sheet defined in claim 1 further characterized by saidheat meltable coating containing coloring matter which is essentiallytransparent to infra-red radiation.

3. A transfer and copy sheet combination for use in a thermographiccopying process in which the transfer sheet serves as a tensioningmember, said combination including a heat meltable coating on saidtransfer sheet, a mineral coating on said copy sheet, said coating onsaid transfer sheet facing toward said copy sheet, and said coating onsaid copy sheet facing away from said transfer sheet.

4. The transfer and copy sheet defined in claim 3 further characterizedby a coloring pigment in said heat meltable coating.

5. In the process of imaging a copy sheet comprising the steps ofsuperposing original infrared radiationabsorbing images together with acopy sheet and a transfer sheet having a heat-transferable imaginglayer, the imaging layer being in intimate surface contact with thesurface of the copy sheet, and applying thereto infrared radiationswhich are absorbed by the original images and converted to heat patternsin the shapes of said images, thereby heating corresponding portions ofthe imaging layer and causing them to melt and transfer to the copysheet in areas corresponding to the locations and shapes of the originalimages, the improvement which comprises using as the transfer sheet onewhich is free of materials that absorb suflicient amounts of infraredradiation on instantaneous exposure thereto to cause transfer of theimaging layer and is comprised of a thin paper foundation having on onesurface thereof a non-melting, non-transferable plastic intermediatelayer and a top heat-transferable imaging layer based upon wax bindermaterial, said transfer sheet being heat resistant and dimensionallystable at the melting temperature of the said imaging layer whereby theportions of the imaging layer that are transferred to the copy sheetform clear and uniform images.

References Cited by the Examiner UNITED STATES PATENTS Newman 11736Miller 25065 Roshkind 250-65 Tien 25065 Clark 117-36.4

4 2,999,035 9/1961 Sahler 250-65 X 3,024,362 3/1962 Sus et a1. 250-653,037,879 6/1962 Newman et a1 11736.1

FOREIGN PATENTS 722,023 1/ 1955 Great Britain.

RALPH G. NILSON, Primary Examiner.

W. F. LINDQUIST, I. W. LAWRENCE, H. S. MILLER, 10 Assistant Examiners.

1. A TRANSFER SHEET FOR THERMOGRAPHIC COPYING IN WHICH THE TRANSFER SHEET SERVES AS A TENSIONING BELT AND IS EXPOSED TO THE DIRECT RADIATION OF A SOURCE OF RADIATION, SAID TRANSFER SHEET COMPRISING: A PAPER BASE, A CLEAR PLASTIC COATING ON SAID BASE, AND A HEAT MELTABLE COATING ON SAID PLASTIC HAVING A MELTING POINT SUBSTANTIALLY LOWER THAN THE MELTING POINT OF SAID PLASTIC COATING.
 3. A TRANSFER AND COPY SHEET COMBINATION FOR USE IN A THERMOGRAPHIC COPYING PROCESS IN WHICH THE TRANSFER SHEET SERVES AS A TENSIONING MEMBER, SAID COMBINATION INCLUDING A HEAT MELTABLE COATING ON SAID TRANSFER SHEET, A MINERAL COATING ON SAID COPY SHEET, SAID COATING ON SAID TRANSFER SHEET FACING TOWARD SAID COPY SHEET, AND SAID COATING ON SAID COPY SHEET FACING AWAY FROM SAID TRANSFER SHEET.
 5. IN THE PROCESS OF IMAGING A COPY SHEET COMPRISING THE STEPS OF SUPERPOSING ORIGINAL INFRARED RADIATIONABSORBING IMAGES TOGETHER WITH A COPY SHEET AND A TRANSFER SHEET HAVING A HEAT-TRANSFERABLE IMAGING LAYER, THE IMAGING LAYER BEING IN INTIMATE SURFACE CONTACT WITH THE SURFACE OF THE COPY SHEET, AND APPLYING THERETO INFRARED RADIATIONS WHICH ARE ABSORBED BY THE ORIGINAL IMAGES AND CONVERTED TO HEAT PATTERNS IN THE SHAPES OF SAID IMAGES, THEREBY HEATING CORRESPONDING PORTIONS OF THE IMAGING LAYER AND CAUSING THEM TO MELT AND TRASFER TO THE COPY SHEET IN AREAS CORRESPONDING TO THE LOCATIONS AND SHAPES OF THE ORIGINAL IMAGES, THE IMPROVEMENTWHICH COMPRISES USING AS THE TRANSFER SHEET ONE WHICH IS FREE OF MATERIALS THAT ABSORB SUFFICIENT AMOUNTS OF INFRARED RADIATION ON INSTATANEOUS EXPOSURE THERETO TO CAUSE TRANSFER OF THE IMAGING LAYER AND IS COMPRISED OF A THIN PAPER FOUNDATION HAVING ON ONE SURFACE THEREOF A NON-MELTING, NON-TRANSFERABLE PLASTIC INTERMEDIATE LAYER AND A TOP HEAT-TRANSFERABLE IMAGING LAYER BASED UPON WAX BINDER MATERIAL, SAID TRANSFER SHEET BEING HEAT RESISTANT AND DIMENSIONALLY STABLE AT THE MELTING TEMPERATURE OF THE SAID IMAGING LAYER WHEREBY THE PORTIONS OF THE IMAGING LAYER THAT ARE TRANSFERRED TO THE COPY SHEET FORM CLEAR AND UNIFORM IMAGES. 